DS1923 datasheet(13/52 Pages) DALLAS

13 / 52 page

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

13 of 52

Figure 4. 64-BIT LASERED ROM

MSB

LSB

8-Bit

CRC Code

48-Bit Serial Number

8-Bit Family

Code (41h)

MSB

LSB

MSB

LSB

MSB

LSB

MEMORY

The memory map of the DS1923 is shown in Figure 5. The 512 bytes general-purpose SRAM are located in pages

0 through 15. The various registers to set up and control the device fill page 16 and 17, called Register Pages 1

and 2 (details in Figure 6). Pages 18 and 19 provide storage space for calibration data. The "data log" logging

memory starts at address 1000h (page 128) and extends over 256 pages. The memory pages 20 to 127 are

reserved for future extensions. The scratchpad is an additional page that acts as a buffer when writing to the

SRAM memory or the register page. The data memory can be written at any time. The calibration memory holds

data from the device calibration that can be used to further improve the accuracy of temperature and humidity

readings. See the Software Correction Algorithm sections for details. The last byte of the calibration memory page

stores an 8-bit CRC of the preceding 31 bytes. Page 19 is an exact copy of the data in page 18. While the user can

overwrite the calibration memory, this is not recommended. See the Security by Password section for ways to

protect the memory. The access type for the register pages is register-specific and depends on whether the device

is programmed for a mission. Figure 6 shows the details. The data log memory is read-only for the user. It is written

solely under supervision of the on-chip control logic. Due to the special behavior of the write access logic (write

scratchpad, copy scratchpad) it is recommended to only write full pages at a time. This also applies to the register

pages and the calibration memory. See the Address Register and Transfer Status section for details.

Figure 5. DS1923 MEMORY MAP

32-Byte Intermediate Storage Scratchpad

ADDRESS

0000H to

001FH

32-Byte General-Purpose SRAM (R/W)

Page 0

0020H to

01FFH

General-Purpose SRAM (R/W)

Pages 1

to 15

0200H to

021FH

32-Byte Register Page 1

Page 16

0220H to

023FH

32-Byte Register Page 2

Page 17

0240H to

025FH

Calibration Memory Page 1 (R/W)

Page 18

0260H to

027FH

Calibration Memory Page 2 (R/W)

Page 19

0280H to

0FFFH

(Reserved For Future Extensions)

Pages 20 to 127

1000H to

2FFFH

Data Log Memory (Read-Only)

Pages 128

to 383

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